(Grant Gustin) learns that Captain Cold (guest star Wentworth Miller) and Heat Wave (guest star Dominic Purcell) have returned to Central City. This time Snart has brought along his baby sister Lisa (guest star Peyton List) to help wreak havoc on the city

Because speedster has travelled back in time in episode 15, he will set off a series of events during Tuesday's episode that ultimately alters what happened previously.

In Out Of Time, Cisco figures out that Harrison Wells is the Reverse Flash, and the time travel bandit kills him. Iris and Barry finally confess their feelings to each other and reveals that he is the speedster, before he falls back in time.

"The first time something changes, the day starts to change," Grant Gustin told Entertainment Weekly. "It starts as the same day, but it's also not the same day pretty much right away, because he realizes what has happened and that in itself changed the course of the day."

The actor also teased that Wells secret will be out in the upcoming episodes.

"He is going to find out about the doctor in the next couple of episodes," Gustin revealed. "Joe [Jesse L. Martin] and Allen refocus all of their energy on Wells."

The speedster will actually become suspicious of the doctor in tonight's episode, though Tom Cavanagh, said that the truth coming out won't make Wells's goal to get home more difficult to obtain. "Harrison is not as dumb as he looks," he said.

"The truth that Wells is the man in the Yellow suit will naturally be devastating to Barry, which makes his job in getting to the truth all the more difficult. Allen still has a hard time not liking him, even after he learns the truth," Gustin said.

Also, because of the time shift, Iris (Candice Patton) admitting that she is in love with Barry, will never happen.

"It's a difficult dynamic between Iris and Allen, and also Iris and the red streak, she is getting closer and closer to figuring it out and I think those questions will be answered by the end of the season for sure," Candice Patton teased.